/*
This file implements the two dimensional Perlin Noise.
The source code is obtained from the website at http://mrl.nyu.edu/~perlin/doc/oscar.html.
In this project,we use the Perlin Noise to generating synthetic DEMs to check the correctness of our proposed variant.
*/

#include <stdlib.h>
#include <math.h>
#include <iostream>
#include "perlin.h"

#define B 0x100
#define BM 0xff

#define N 0x1000
#define NP 12   /* 2^N */
#define NM 0xfff

static int p[B + B + 2];
static float g3[B + B + 2][3];
static float g2[B + B + 2][2];
static float g1[B + B + 2];
static int start = 1;

static void init(void);

#define s_curve(t) ( t * t * (3. - 2. * t) )

#define lerp(t, a, b) ( a + t * (b - a) )

#define setup(i,b0,b1,r0,r1)\
  t = vec[i] + N;\
  b0 = ((int)t) & BM;\
  b1 = (b0+1) & BM;\
  r0 = t - (int)t;\
  r1 = r0 - 1.;

float noise2(float vec[2])
{
  int bx0, bx1, by0, by1, b00, b10, b01, b11;
  float rx0, rx1, ry0, ry1, *q, sx, sy, a, b, t, u, v;
  register int i, j;

  if (start) {
    start = 0;
    init();
  }

  setup(0, bx0, bx1, rx0, rx1);
  setup(1, by0, by1, ry0, ry1);

  i = p[bx0];
  j = p[bx1];

  b00 = p[i + by0];
  b10 = p[j + by0];
  b01 = p[i + by1];
  b11 = p[j + by1];

  sx = s_curve(rx0);
  sy = s_curve(ry0);

#define at2(rx,ry) ( rx * q[0] + ry * q[1] )

  q = g2[b00]; u = at2(rx0, ry0);
  q = g2[b10]; v = at2(rx1, ry0);
  a = lerp(sx, u, v);

  q = g2[b01]; u = at2(rx0, ry1);
  q = g2[b11]; v = at2(rx1, ry1);
  b = lerp(sx, u, v);

  return lerp(sy, a, b);
}

static void normalize2(float v[2])
{
  float s;

  s = sqrt(v[0] * v[0] + v[1] * v[1]);
  v[0] = v[0] / s;
  v[1] = v[1] / s;
}

static void normalize3(float v[3])
{
  float s;

  s = sqrt(v[0] * v[0] + v[1] * v[1] + v[2] * v[2]);
  v[0] = v[0] / s;
  v[1] = v[1] / s;
  v[2] = v[2] / s;
}

static void init(void)
{
  int i, j, k;

  for (i = 0; i < B; i++) {
    p[i] = i;
    
    g1[i] = (float)((rand() % (B + B)) - B) / B;

    for (j = 0; j < 2; j++)
      g2[i][j] = (float)((rand() % (B + B)) - B) / B;
    normalize2(g2[i]);

    for (j = 0; j < 3; j++)
      g3[i][j] = (float)((rand() % (B + B)) - B) / B;
    normalize3(g3[i]);
  }

  while (--i) {
    k = p[i];
    p[i] = p[j = rand() % B];
    p[j] = k;
  }

  for (i = 0; i < B + 2; i++) {
    p[B + i] = p[i];
    g1[B + i] = g1[i];
    for (j = 0; j < 2; j++)
      g2[B + i][j] = g2[i][j];
    for (j = 0; j < 3; j++)
      g3[B + i][j] = g3[i][j];
  }
}
